experiment showing carbon dioxide necessary photosynthesis

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Experiment to show that carbon dioxide is needed for photosynthesis

In my school test, the question is as follows:

• Will the experiment work satisfactorily?
• What alterations can you make to obtain expected result?

What I wrote:

Yes, it will work satisfactorily. Lime water absorbs carbon dioxide and hence there is no carbon dioxide for the leaf and hence photosynthesis does not take place and no starch is prepared. Hence on iodine test, the presence of starch is negative and thus proves that carbon dioxide is required for photosynthesis.

We can put half of the leaf inside the flask and half of it outside. So, the inside part will not show presence of starch and the outside part will show presence of starch.

[Note]: It was marked incorrect by my biology teacher. It got it reviewed by another biology teacher and HE SAID WHAT I WROTE IS CORRECT and the teacher who marked it wrong gave the opinion as follows:

It will not work satisfactorily because lime water does not absorb carbon dioxide. [which to me, seems incorrect as lime water ABSORBS carbon dioxide]

The alteration is that you have to use Potassium Hydroxide instead of lime water. [which to me, seems incorrect too since both lime water and potassium hydroxide absorbs carbon dioxide and then there is no need to use potassium hydroxide when lime water works!]

Now I am confused what is correct and what should I write in my final examination?? Please help. Any help will be appreciated, Thank you.

• photosynthesis

• 1 $\begingroup$ Not an expert answer but from experience, I’ve seen limewater absorb $\ce{CO_2}$ mostly when $\ce{CO_2}$ is bubbled through the solution. However, in respirometers, KOH is used to absorb any neighboring $\ce{CO_2}$ in the chamber. Analogically thinking, it seems to me that limewater won’t be very efficient in removing $\ce{CO_2}$ from the flask in your experiment. Thus, you are correct in stating limewater absorbs $\ce{CO_2}$, but it might not work “satisfactorily,” making the teacher’s answer correct. For q2, I feel you should combine both your teacher’s and your answers. A control is needed. $\endgroup$ –  lightweaver Commented Apr 2, 2016 at 5:23

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Carbon Dioxide Is Essential for Photosynthesis

To show that carbon dioxide is essential for photosynthesis.

Introduction

Photosynthesis is a fundamental biological process that occurs in plants, algae, and some bacteria, enabling them to convert light energy from the sun into chemical energy in the form of glucose and other organic molecules. During photosynthesis, plants use sunlight, water, and carbon dioxide to produce glucose (a simple sugar) and oxygen. External factors affecting photosynthesis include light, carbon dioxide concentration, temperature, and water availability.

Carbon dioxide is essential for photosynthesis because it serves as the primary source of carbon atoms used to build organic molecules like glucose in plants.

Experiment Procedure

To demonstrate the experiment on carbon dioxide is essential for photosynthesis, we need to follow the given procedure:

• Choose a destarched potted plant (e.g., Tecoma, Balsam, Amaranthus, Salvia).
• Fill 1/5 th of a boiling tube with KOH solution.
• Insert half of an intact leaf into the tube, ensuring it doesn’t touch the solution.
• Secure the tube with a clamp, sealing it with petroleum jelly.
• Expose the setup to sunlight for a few hours.
• Boil 150 mL water, then immerse the detached leaf and let it cool to 60°C.
• Transfer the leaf to alcohol in another boiling tube.
• Place the tube in a beaker of hot water until the leaf turns colourless.
• Dip the leaf in iodine solution in a petri dish after washing.
• After about five minutes, remove the leaf, wash it, and observe.

This experiment strongly shows how important carbon dioxide is for photosynthesis. The clear difference in starch between the lit and pale leaves highlights its key role. This emphasises how carbon dioxide is closely connected to making food in plants, showing how crucial it is for their growth and the environment.

FAQs on Carbon Dioxide Is Essential for Photosynthesis

Q.1 why is carbon dioxide important for photosynthesis.

Ans. Carbon dioxide is a crucial ingredient in photosynthesis because it provides the carbon atoms necessary for building organic molecules, such as glucose, which are essential for plant growth and energy storage.

Q.2 How does carbon dioxide enter the plant for photosynthesis?

Ans. Carbon dioxide enters the plant through tiny pores called stomata, primarily located on the leaves. These openings allow carbon dioxide to diffuse into the plant’s cells, where photosynthesis occurs.

Q.3 What happens to carbon dioxide during photosynthesis?

Ans. During photosynthesis, carbon dioxide is used by plants, along with water and sunlight, to produce glucose and oxygen. This process occurs in chloroplasts within plant cells.

Q.4 How does the availability of carbon dioxide affect plant growth?

Ans. The availability of carbon dioxide directly impacts the rate of photosynthesis and, consequently, plant growth. Higher concentrations of carbon dioxide generally lead to increased photosynthetic activity and enhanced growth.

Q.5 Can photosynthesis occur without carbon dioxide?

Ans. Photosynthesis cannot occur without carbon dioxide. It’s a necessary raw material for the process, and without it, plants wouldn’t be able to synthesise the organic compounds needed for growth and survival.

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Photosynthesis: Step by Step Guide (Experiments Included)

• May 10, 2021
• Science Facts

Have you ever wondered how plants eat or drink? How do they get energy? Well, just like we need food and water to live, plants do too. However, unlike humans, they make their food from sunlight and carbon dioxide! How? They do it by a process known as photosynthesis.

This article will explore photosynthesis and learn the difference between chemical compounds like carbon dioxide, sugar, and energy. We’ll look at how plants store energy as starch.

What is Photosynthesis?

Plants and a few other organisms “put together” organic matter from carbon dioxide and water, using the energy of sunlight to power the process.

It is derived from the Greek word, ‘photo’ meaning light, and ‘synthesis’ meaning putting together.

Plants are the basis for almost all life on Earth: animals (including humans) either eat plants or eat other animals that eat plants. Also, plants provide us with oxygen.

Ingredients for Photosynthesis

When you’re hungry, you may ask your mom for food. However, plants can’t do that. So, they use the nutrients and water present in the soil, light energy from the sun, and Carbon Dioxide from the air to form a compound called glucose.

Glucose is a sugar that plants need to survive on. It’s their form of food, like you eat rice or noodles, they consume glucose for energy!

Why is photosynthesis important for life?

All living organisms on Earth are dependent on photosynthesis. Plants would not survive without photosynthesis, and thus, neither would animals that depend on the plants for food. Autotrophs, like plants and algae, produce glucose through photosynthesis.

Animals cannot do this. Therefore, they eat plants and use this energy in the process of cellular respiration. Otherwise, they get their energy through organisms that feed off autotrophs.

Organisms, who cannot synthesize their own food independently, are known as heterotrophs. These include:

• Herbivores such as cows and deer, who eat plants.
• Carnivores such as lions and wolves, who eat other animals.
• Omnivores such as humans and bears, who eat both plants and animals.

So, the plants are the start of all food chains and sustain all organisms. For example:

How Green Plants Make their Food

Green plants carry out photosynthesis by using a special green pigment called chlorophyll.

The chlorophyll inside the leaves captures the energy from sunlight, combines carbon dioxide with water, and makes sugar (glucose).

The plant transports this simple sugar to every part of its body. All in all, the steps involved in this process are:

●     Absorption of Light Energy

Have you seen the sunflower plant moving towards the sun when kept in the shade? This is because the trapping of light energy is key to the process of photosynthesis.

Without sunlight, there will be no energy to make food. So, the first and most crucial step is that the chlorophyll in green plants absorbs sunlight.

●     Conversion of Light Energy to Chemical Energy

Plants cannot directly utilize sunlight. So, they convert it into ATP (Adenosine TriPhosphate), a form of chemical energy.

When sunlight is absorbed, the chlorophyll atoms become photochemically excited and lose an electron, thus undergoing a process known as oxidation.

This electron is then used to convert non-usable sources of energy such as ADP and NADP+ compounds to primary chemical energy sources such as ATP and NADPH.

Then, to replace the electron lost in by the photochemically excited chlorophyll, the water absorbed by the plants splits into its two components- Hydrogen and water.

Since, hydrogen has only one electron, it breaks into protons and electrons, and then it uses the electron to bring the chlorophyll back to its original state.

This completes the process of conversion to immediate chemical energy, which is used to form glucose.

●     Conversion of Carbon Dioxide to Glucose

When the water splits into hydrogen and oxygen, it undergoes an oxidation reaction as it loses Hydrogen. Similarly, carbon dioxide undergoes a reduction reaction as it gains electrons. So, as a result, water is converted to oxygen gas, and carbon dioxide is converted to glucose.

This is known as a redox reaction. Observe the following diagram to understand it better. A is water converting to oxygen, and B is Carbon Dioxide converting to simple carbohydrates (glucose) in photosynthesis.

Photosynthesis Chemical Reaction in Words

Now that you understand how reactions occur and the resultant products are formed, it’s essential to know how to put them into words. One glance over this summarises everything explained above- that is what a chemical formula does!

The above equation represents the following chain of processes:

• Sunlight coming in contact with the chlorophyll in the thylakoid membrane of the chloroplast.
• Chlorophyll molecules get excited, and water splits into hydrogen and oxygen.
• Electrons from hydrogen (from the water) combine with Carbon Dioxide. This process is known as reduction, and glucose is formed.
• Oxygen is a by-product. Since it is of no use, it is excreted or thrown out from the cell.

Chemical Reaction Formula for Photosynthesis

Physical chemistry can be tricky because there are so many terms and factors to keep track of. So, you must understand these simple equations before you are allowed to work with natural chemicals.

A chemical equation is simply a list of all the chemical reactants and products and their relative quantities at its heart.

Chemicals are complex systems that can exist in very different states. Nonetheless, they can easily be represented as simple lists of these elements and their numbers. So, one can describe photosynthesis as:

However, this isn’t a balanced equation. According to the Law of Conservation of Mass, mass can neither  be created nor destroyed. Count the number of Carbon atoms on the reactant side (the left side.)

Now, count the number of Carbons on the product side (the right side.) One carbon can’t magically turn into six carbons, right? So, to rectify it, form a balanced equation of the reaction.

6CO 2  +  6H 2 O  →  C 6 H 12 O 6  + 6O 2

Note that the number before the Carbon Dioxide, Water, and Oxygen represents the individual compound molecules.

Therefore, the number of Carbons on both sides of the equation is 6, oxygens are 18 (twelve from Carbon Dioxide and six from water), and hydrogens is 12.

Since the total number of atoms from each element are equal on the reactant and product side, this is now a balanced equation!

What does photosynthesis produce?

The release of chemical energy due to the formation of ATP and NADPH compounds, and the synthesis of oxygen, are light-dependent reactions.

However, a series of light-independent reactions- constituting the Calvin Cycle, actually form the food.

How is glucose formed? Does excess glucose undergo some changes? Read to find out.

The Calvin Cycle

This cycle consists of a series of light-independent reactions- which means they do not directly require sunlight to work. So, they can take place at night or day. They include:

• Carbon Fixation

One of the most critical functions of carbon is that it can be converted from Inorganic compounds (carbon dioxide in the atmosphere) to organic compounds such as G3P and glucose. This process is known as Carbon fixation.

Before glucose is formed in plants, first, they synthesize an intermediate compound known as glyceraldehyde-3-phosphate. Here, the carbon from carbon dioxide is used to manufacture G3P- C 3 H 7 O 6 – a three-carbon molecule.

• Formation of glucose and other carbohydrates

G3P is a raw material used in the formation of glucose. The Calvin Cycle involves 18 ATP and 12 NADPH molecules to synthesize one molecule of C 6 H 12 O 6 (glucose).

It’s also used to form starch, sucrose, and cellulose, depending on the plant’s needs.

Starch also plays a significant role in nutrition in animals. When animals eat plants, their digestive processes break down the starch present to form glucose again.

This glucose is then used as a source of energy for metabolic processes. So, the starch in animals sustains the plant, the herbivore, the carnivore, and the decomposer.

What happens to excess carbohydrates which are not utilized immediately?

When carbohydrates are not utilized immediately, they are stored in various parts of the plant’s body in the form of starch. It’s a polysaccharide- a compound formed by binding a chain of

glucose molecules together. It stores a significant amount of energy for cell metabolism.

The stored starch gives the cell energy to perform all the processes necessary for its survival. Any unused energy is stored as a fat deposit.

Factors that affect the Rate of Photosynthesis

Just as human beings need various nutrients to survive, plants need several environmental conditions for photosynthesis to happen appropriately.

Even if one of the optimum requirements is affected, so is the rate of photosynthesis in plants. So, photosynthesis is based upon several factors. They include:

1. Light Intensity

If the light energy provided to plants is too low, the plants cannot photosynthesize properly. At the optimum amount of sunlight, the plant makes the food faster.

However, the speed slows down again if the light energy given increases above the plant’s maximum tolerance level. In winter or colder areas, the rate decreases and falls to zero at night.

Therefore, light intensity plays a vital role in the rate of photosynthesis.

2. Carbon Dioxide Concentration

Up to the maximum tolerance of carbon dioxide in plants, increasing the amount of exposure to gas maximizes the rate of photosynthesis.

After that, increasing carbon dioxide concentration in the air will not affect the plants.

This is because the plants can only intake a certain amount of carbon dioxide to convert into glucose. So, one can represent the rate of photosynthesis as:

3. Temperature

In photosynthesis, a lot of enzymes need to work to fulfill the requirement of energy. However, they can only work at the optimum temperature.

Raising the temperature increases kinetic energy. So the molecules start moving at a higher speed and collide faster, increasing the rate of photosynthesis.

Like in all the other cases, very high temperature is just as bad as very high temperature. In both cases, the enzymes will gradually be destroyed, and the photosynthesis will eventually stop.

Energy Result of Photosynthesis

As we have seen, there are two types of reactions in photosynthesis- the light reactions and the dark reactions.

The light-dependent processes synthesize energy in the form of ATP and NADPH.

The dark reaction uses already made energy to manufacture glucose and other carbohydrates, which are further used in metabolic processes required for the plant’s survival.

So, let’s look at these chemical processes from the perspective of energy used and released.

1. Light-Dependant Reactions

Sunlight gives plants the energy to photochemically excite the chlorophyll, which leads to the splitting of water. This allows the conversion of ADP and NADP+ molecules into ATP and NADPH, which can be used in other processes.

2H 2 O + 2 NADP+ + 3 ADP + 3 P i + Light Energy → 2 NADPH + 2 H + + 3 ATP + O 2

2. Dark Reactions

The energy synthesized in the light-dependant reactions is used to reduce carbon dioxide and form glucose. The carbon fixation process takes place here; that is, the carbon gets converted from an inorganic form to an organic compound.

3 CO 2 + 9 ATP + 6 NADPH + 6 H + → C 3 H 6 O 3 -phosphate + 9 ADP + 8 P i + 6 NADP+ + 3 H 2 O

Further, it takes 18 ATP and 12 NADPH compounds to convert the G3P molecule into glucose.

3. Respiration

When the glucose molecule is formed, the plant performs a process known as respiration. The glucose molecule is combined with oxygen and breaks down into carbon dioxide and water.

In this process, a considerable amount of energy is released.

This energy is used to help the plant perform all its metabolic functions needed to survive. It’s a constant cycle, which the following diagram can explain:

How Do Plants Absorb Energy From the Sun?

As we’ve seen, photosynthesis cannot take place without energy from the Sun. So, the plants have a mechanism set in place to observe light energy.

This is done by the pigment chlorophyll, present in chloroplasts, present in the cells of green leaves of plants. Let’s look at the structure of the chloroplast to help you understand.

Sunlight has a lot of components. All the parts have a certain amount of energy. The main components of sunlight used by the plants are blue, red, and green.

With the thylakoid’s help in the chloroplasts (observe the diagram), which contain chlorophyll, the light energy is absorbed—specifically, the blue and red components.

The green is reflected into the environment. Now, can you answer the question, ‘why do plants look green?’ It’s because of the reflected green light!

Look at the diagram again. Can you see that the thylakoids are present in stacks? These are known as grana, which is the site of converting light energy to chemical energy!

The aqueous fluid surrounding them is known as the stroma. The transformation is completed here.

Where Do Plants Get the Carbon Dioxide Needed?

Just like we breathe through our noses, plants have millions of tiny openings on the surface of their leaves. These are known as stomata.

These stomata pores are protected by a pair of guard cells, which regulate the opening and closing of these pores.

When they do open, the atmosphere’s carbon dioxide flows through the stomata, from where it’s sent to the chloroplast- the site of photosynthesis.

Various environmental stimuli control the guard cells. When all the optimum conditions (water and sunlight) are present, the guard cells swell and curve.

This movement is because it takes in water through a process known as osmosis, which triggers the opening of the guard cells and allows the carbon dioxide to enter.

At night, when there’s no light or the plant wants to conserve water, the stomatal pores lose water through osmosis.

This causes the stomata to become straight, and once again, they are closed. One can also show this process with a diagram:

Why Do Plants Produce Glucose?

Now that we know how plants produce glucose, it’s essential to understand why? Why are these six-carbon molecules so crucial for life? Let’s find out.

1.   Storage

Sun is essential for the release of energy. Therefore, during the winter or the night, when there is not enough sunlight, the plant uses the glucose stored in various parts of the plant.

The process of respiration takes place, and the energy for metabolic processes is released without the presence of the Sun.

Without the stored glucose, the plant would’ve died during the night or the long winters.

2.   Seed Formation and Flowering

Glucose is stored in the seed in the structures known as cotyledons. They allow the seedling to stay alive even deep inside the soil, without leaving to synthesize food.

Furthermore, they provide the energy required for germination and encourage leaf growth. Moreover, glucose stored in some plants also helps in the flowering of some unique plants.

Hyacinths, daffodils, and tulips are some plants that depend upon the glucose to flower. These beautiful flowers attract pollinating agents towards them, which helps the plant to reproduce.

3.   Formation of other nutrients

Several glucose molecules combine to form starch- a complex carbohydrate present in plants.

They also react with nitrates present in the soil to form amino acids, which eventually form proteins. Carbohydrates and proteins are major nutrients for both humans and plants.

Thus, glucose plays an essential role in nutrition.

4.   Circadian Rhythms

Plants need to maintain their body temperature and stay in tune with the day-and-night cycles. So, the formation of glucose in the day and respiration during the night helps the plant to maintain its daily clock and energy reserves.

How Do Plants Eat?

Now, since glucose has been synthesized, the next step is transportation and utilization. So, the sugar is transported through various parts of the plant, where it’s needed.

A vascular tissue known as phloem accomplishes this movement.

Then, similar to humans, cellular respiration takes place in plants as well. Plants convert glucose and other sugars, in the presence of oxygen, into energy.

Carbon Dioxide and water are by-products of this process. Just like you need the energy to breathe, walk, run, study, and survive- plants need it for:

• Growth processes
• Making more food
• Other cellular maintenance functions

So, just like we eat our food, plants synthesize glucose and other carbohydrates and convert them to energy!

Since it doesn’t require light energy, it can take place during the day or the night. So, the plant doesn’t starve.

Role of Leaves in Photosynthesis

Leaves are sites of photosynthesis. So, they have a series of features that help them perform their function efficiently. Leaves have adapted to the environment in various ways, such as:

• Large Surface Area

Broader leaves can absorb more light energy and thus, increase the surface area for photosynthesis.

• Shorter Width

The leaves are thin so that the absorbed carbon dioxide has to travel a short distance to reach the chloroplasts (sites of photosynthesis).

Otherwise, a considerable amount of energy would have to be spent on CO 2 transport, which the plant couldn’t afford.

Observe the given diagram. Have you ever touched a vein? Is it harder or softer than the surface of the leaf?

Veins in the leaf provide support, and transport food, water, and minerals as well. They are extensions of the vascular bundles- Xylem (which transports water and minerals) and Phloem (which transports synthesized food.)

• Chloroplasts

Of course, the main adaptation of leaves is the chloroplasts with the pigment chlorophyll inside of them.

These absorb light energy, then convert it into a usable form- chemical energy. Without these small components, photosynthesis wouldn’t take place, and life wouldn’t exist.

Role of Water in Photosynthesis

• Converts NADP+ to NADPH

When photosynthesis takes place, water splits into its components- hydrogen and oxygen. The H + ions are then used to reduce the NADP molecules to NADPH molecules, which can be used to synthesize glucose. It also eventually leads to the formation of ATP- the energy currency of the cell.

• Provides Oxygen

The oxygen, which is obtained from the splitting of water, is released into the atmosphere and used by animals and humans for respiration. Most living organisms on the face of this planet need this oxygen released by plants to survive.

• Reduces chlorophyll

When the sunlight hits chlorophyll, it becomes photochemically excited, loses an electron, and undergoes oxidation. So, to return to its original state- water donates an electron and acts as a reducing agent.

Do All Plants Photosynthesize?

We sometimes look at photosynthesis as the defining characteristic in plants. However, there are some plants, which do not have chlorophyll and do not perform photosynthesis.

Instead, they choose to get their energy by stealing from their neighboring plants. These are known as holoparasites.

They are entirely dependent on their host and obtain nutrients required from living off of them. So, they do not need to perform photosynthesis, but the host eventually dies due to the continuous stealing of nutrients by the parasites.

Photosynthesis in Oceans

Have you ever wondered how marine plants perform photosynthesis in seas or oceans, where there is a limited amount of light and carbon dioxide?

So, most marine plants stay near the surface of the water to fulfil their requirements. Furthermore, chemical molecules known as phycobiliproteins are present in some tiny organisms known as cyanobacteria, which absorb the light available in the ocean and convert it into light energy that the chlorophyll can use.

Marine organisms release half the Earth’s oxygen, even though their biomass is less in magnitude than bulky terrestrial organisms. They reproduce faster, a new generation every day or two! More significant numbers help in the process of photosynthesis as well.

Science Experiments that Prove Photosynthesis in Plants

Experiments on photosynthesis in plants are fascinating. Children will soon find out that there is no need to fear biology because it’s been fun all along. The four experiments on photosynthesis in this article will create joy and excitement among children who love science.

Experiment #1

Aim: To prove that plants need sunlight to grow

Materials Required:  A potted plant, a boiling tube, 70% alcohol, iodine solution, bunsen burner, forceps, beaker, water, dropper, black paper, and a petri dish.

• Place the potted plant in the dark for about 72 hours. This inhibits the process of photosynthesis, and all the leaves become free of starch.
• After three days, take a strip of black paper and put it on a section of one of the potted plant leaves on both sides.
• Put the plant in the sunlight for a few hours.
• Detach the partially covered leaf from the plant and remove the black covering.
• Boil this leaf in a 70% alcohol solution using a bunsen burner until it loses its green color. This is because we are removing chlorophyll.
• Wash the leaf with water and add iodine solution with a dropper.

Observation: The whole leaf turns blue-black, except for the section covered with black paper. This is because iodine changes color in the presence of starch. However, since the covered portion did not come in contact with the sun, it didn’t photosynthesize, and thus, starch wasn’t present.

Conclusion: We realize that plants need sunlight to photosynthesize and manufacture food.

Experiment #2

Aim: To prove that Carbon Dioxide is necessary for photosynthesis.

Materials Required: A healthy potted plant with long and narrow leaves, Potassium Hydroxide solution, 70% alcohol solution, a jar with a large mouth and cork, grease or vaseline, bunsen burner, petri dish.

• Open the jar and pour in a couple of millimeters of potassium hydroxide. This absorbs the carbon dioxide gas present in the atmosphere.
• After three days, choose a long and narrow leaf and put half of it in the jar.
• Seal the jar and make sure it’s airtight. Put grease on the corners of the cork.
• Detach the leaf from the plant and boil it in a 70% alcohol solution using a bunsen burner until it loses its green color.

Observation: The half of the leaf exposed to the air turns blue-black due to the presence of starch. The other half was deprived of CO 2, and therefore, it didn’t form starch.

Conclusion: Carbon Dioxide gas is necessary for the process of photosynthesis.

Experiment #3

Aim:  To prove that oxygen gas is released during photosynthesis.

Materials Required: A large beaker filled with water, a short transparent funnel, pondweed, or an aquatic plant such as Hydrilla, and a test tube.

• Place a few twigs of the aquatic plant into the transparent funnel.
• Immerse the funnel into the beaker full of water.
• Now, fill the test tube until it’s almost overflowing with water. Cover the mouth of the tube with your thumb.
• Invert the test tube and put it over the funnel, as shown in the diagram.
• Place the setup in the sunlight.
• Observe until the test tube is completely filled with gas.
• Take out the test tube carefully without letting the gas out.
• Bring a burning splinter in contact with the gas. Observe.

Observations: After a few hours in sunlight, there are bubbles in the water, proving the presence of a gas. The burning splint reignites with a pop sound when it’s brought in contact with the test tube- confirming the presence of oxygen.

Conclusion: Photosynthesis releases oxygen.

The Conclusion

Next time you see a tree, stop to hug it. It does a lot of work to make sure that we, humans can live by being one of our resources.

Knowing how photosynthesis works and how it nourishes all the animals in the world should help us realize that plants give us life.

Learning about photosynthesis also explains what makes plants unique. With the information and activities in the article, you now understand what photosynthesis is; and what it means to the environment.

One comment

Dear Angela, Great article on photosynthesis. I could comprehend it easily. It’s explanation method was superb.

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Investigating the Need for Chlorophyll, Light & Carbon Dioxide ( CIE IGCSE Biology )

Revision note.

Biology Lead

Investigating the Need for Chlorophyll

• Although plants make glucose in photosynthesis, leaves cannot be tested for its presence as the glucose is quickly used, converted into other substances and transported or stored as starch.
• Starch is stored in chloroplasts where photosynthesis occurs so testing a leaf for starch is a reliable indicator of which parts of the leaf are photosynthesising.
• A leaf is dropped in boiling water to kill the cells and break down the cell membranes
• The leaf is left for 5-10 minutes in hot ethano l in a boiling tube. This removes the chlorophyll so colour changes from iodine can be seen more clearly
• The leaf is dipped in boiling water to soften it
• The leaf is spread out on a white tile and covered with iodine solution
• In a green leaf, the entire leaf will turn blue-black as photosynthesis is occurring in all areas of the leaf
• This method can also be used to test whether chlorophyll is needed for photosynthesis by using a variegated leaf (one that is partially green and partially white)
• The white areas of the leaf contain no chlorophyll and when the leaf is tested only the areas that contain chlorophyll stain blue-black
• The areas that had no chlorophyll remain orange-brown as no photosynthesis is occurring here and so no starch is stored

Testing a variegated leaf for starch

• Care must be taken when carrying out this practical as ethanol is extremely flammable, so at that stage of the experiment the Bunsen burner should be turned off.
• The safest way to heat the ethanol is in an electric water bath rather than using a beaker over a Bunsen burner with an open flame

Investigating the Need for Light

• The same procedure as above can be used to investigate if light is needed for photosynthesis
• Before starting the experiment the plant needs to be destarched by placing in a dark cupboard for 24 hours
• This ensures that any starch already present in the leaves will be used up and will not affect the results of the experiment
• Following destarching, a leaf of the plant can be partially covered with aluminium foil and the plant placed in sunlight for a day
• The leaf can then be removed and tested for starch using iodine
• The area of the leaf that was covered with aluminium foil will remain orange-brown as it did not receive any sunlight and could not photosynthesise, while the area exposed to sunlight will turn blue-black
• This proves that light is necessary for photosynthesis and the production of starch

Investigating the Need for Carbon Dioxide

• Destarch two plants by placing in the dark for a prolonged period of time
• Place one plant in a bell jar which contains a beaker of sodium hydroxide ( which will absorb carbon dioxide from the surrounding air)
• Place the other plant in a bell jar which contains a beaker of water  (control experiment), which will not absorb carbon dioxide from the surrounding air
• Place both plants in bright light for several hours
• Test both plants for starch using iodine
• The leaf from the plant placed near sodium hydroxide will remain orange-brown as it could not photosynthesise due to lack of carbon dioxide
• The leaf from the plant placed near water should turn blue-black as it had all necessary requirements for photosynthesis

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Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

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• Photosynthesis

Guide students to measure the change in carbon dioxide (in a closed system) with a carbon dioxide sensor to facilitate an understanding of the relationship between carbon dioxide, respiration, and photosynthesis in plants.

Grade Level: Middle School

Subject: Life Science

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Photosynthesis (Middle School)

Measure the change in carbon dioxide (in a closed system) with a carbon dioxide sensor to facilitate an understanding of the relationship between carbon dioxide,...

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How to Visualize Photosynthesis: A Simple Science Experiment

Looking for a science experiment that visualizes how photosynthesis works? Check out this simple outdoor science project that requires very few materials and can be done at home or school!

Introducing kids to the process of photosynthesis can be tricky, as this complex chemical process isn’t easily seen; it just kind of “happens” all around us, all the time. The idea that a living organism takes one type of gas from the atmosphere and, with the help of water and sunlight, makes an entirely new type of gas that is essential to our survival, along with food for itself seems almost magical. When looking for a way to help my kids understand how plants perform photosynthesis, I stumbled upon an easy and free experiment that allows them to see the oxygen gas created by green plants.

What is Photosynthesis?

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy from the sun into chemical energy in the form of glucose (sugar). It is a complex series of chemical reactions that take place in specialized organelles called chloroplasts, which contain the pigment chlorophyll.

During photosynthesis, carbon dioxide (CO 2 ) from the atmosphere and water (H 2 O) from the soil is combined with light energy to produce glucose and oxygen (O 2 ). This process is essential for life on Earth, as it provides the basis for the food chain and produces the oxygen we breathe.

What is the Chemical Equation for Photosynthesis?

The overall balanced chemical equation for photosynthesis is:

6 CO 2 + 6 H 2 O + light energy → C 6 H 12 O 6 + 6 O 2

where CO 2 is carbon dioxide, H 2 O is water, C 6 H 12 O 6 is glucose, and O 2 is oxygen.

The coefficients in front of each chemical formula give us a bit more information about the “recipe” needed to produce food for the photosynthesizing organism. It takes 6 molecules of carbon dioxide combined with 6 molecules of water in the presence of sunlight to create 1 molecule of glucose and 6 molecules of oxygen.

How Does Photosynthesis Work?

As in most things in science, the process of photosynthesis can be described in even more detail than the general balanced equation shown above. Photosynthesis is a complex process that occurs in two main stages: light-dependent reactions and light-independent reactions (also known as the Calvin cycle). Typically this level of detail wouldn’t be taught to students until high school level biology. Here’s a brief overview of how photosynthesis works in more detail:

Light-dependent reactions:

The first stage of photosynthesis occurs in the thylakoid membrane of the chloroplasts, where light energy is absorbed by chlorophyll and other pigments. This light energy is used to create high-energy molecules such as ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate), which are needed for the second stage of photosynthesis.

Light-independent reactions (Calvin cycle):

The second stage of photosynthesis occurs in the stroma of the chloroplasts, where carbon dioxide is fixed into organic molecules such as glucose. This process is known as the Calvin cycle and requires the ATP and NADPH produced in the first stage. In the Calvin cycle, carbon dioxide molecules are combined with molecules of the 5-carbon sugar ribulose bisphosphate (RuBP) to form an unstable 6-carbon molecule. This molecule is then broken down into two molecules of a 3-carbon sugar, which can be used to create glucose and other organic molecules.

Overall, photosynthesis is a complex biochemical process that converts light energy into chemical energy, producing oxygen and organic molecules as byproducts.

What Types of Organisms Use Photosynthesis?

Photosynthesis is used by a wide range of organisms to produce food. The most well-known photosynthetic organisms are green plants, which use chlorophyll to convert light energy into glucose. However, many other types of organisms use photosynthesis as a source of food, including:

• Algae: These are a diverse group of photosynthetic organisms that can be found in a wide range of environments, including freshwater, marine, and terrestrial habitats. They come in a variety of shapes and sizes, ranging from single-celled organisms to large, multicellular seaweeds.
• Cyanobacteria: These are a group of photosynthetic bacteria that are capable of fixing nitrogen from the atmosphere. They are often found in aquatic environments, but can also be found in soil, on rocks, and in other habitats.
• Photosynthetic bacteria: In addition to cyanobacteria, other types of bacteria are capable of photosynthesis, including purple bacteria and green sulfur bacteria.

For our purposes of creating a simple photosynthesis science experiment, we will be focusing on green plants.

Free Visualizing Photosynthesis Science Experiment Printable

To help make this science experiment more meaningful, I’ve created a free printable that you can use to guide your students’ learning. The printable includes:

• Creation of a hypothesis
• Visual observations before and after the experiment
• Analysis and conclusion questions

To get your copy of this free printable, simply enter your name and email address below!

FREE Visualizing Photosynthesis Science Experiment

Materials needed for visualizing photosynthesis science experiment.

This simple science experiment requires very few materials and can be set up within minutes. Here are the supplies needed to conduct this visualizing photosynthesis science experiment.

• 5-7 freshly picked green leaves
• 5-7 small pebbles or other small objects to weigh down the leaves
• shallow dish or tray with sides
• direct sunlight
• free printable “Visualizing Photosynthesis” student sheets

I have found that the results of this experiment are best when it is conducted outside with access to direct sunlight, as opposed to running the experiment inside in front of a window. However, if you have access to a greenhouse, or have old windows that are not double-paned, this experiment may do well indoors.

Instructions to Conduct the Visualizing Photosynthesis Science Experiment

The initial set-up of this science experiment is quite simple and, depending upon the time of year it is conducted, you may begin to see results within an hour.

• On the free printable provided, make a hypothesis about what you think will happen to the surface of the leaves when left undisturbed in direct sunlight for an hour. 
• Place 5-7 freshly picked leaves face up in a shallow dish or tray.
• Position the dish in direct sunlight.
• Sketch one or two of the leaves chosen for your experiment.
• Place a small pebble on the center of each leaf. Be careful not to cover the entire leaf with your object, as sunlight needs to be able to reach the leaf.
• Pour enough water into the dish to just cover all of the leaves. 
• Allow the leaves to sit undisturbed for an hour in direct sunlight.
• After an hour, observe the leaves.
• Create a second sketch of the leaves you chose at the beginning of the experiment, noting any differences that have occurred. Make sure to take a close look at the surface and edges of the leaves.
• If no changes have occurred, allow the leaves to sit undisturbed for another hour in direct sunlight, then reobserve.
• Answer the questions that are found on the visualizing photosynthesis printable .

Typical Results of the Visualizing Photosynthesis Science Experiment

Once the leaves have sat undisturbed for one hour in direct sunlight, learners should see small bubbles form on the edges and tops of the leaves. These bubbles contain oxygen and are the direct result of photosynthesis. The purpose of the water in the experiment is to visualize the oxygen gas; without the water, the gas bubbles would not be trapped and would simply enter the air.

Be sure to have the students complete the questions on my free printable on their own or in small groups before discussing it as a class. It may be helpful to display the chemical equation for photosynthesis to remind students that the creation of oxygen gas is part of photosynthesis.

More Science Experiments About Plants

If you enjoyed this simple science experiment about plants, you may also like the following:

• How to Propagate Plants in Water with Kids
• How to Regrow Vegetables from Food Scraps
• How to Grow Your Own Popcorn
• Teaching Kids How to Grow Potatoes

How to Visualize Photosynthesis: A Science Experiment

Instructions

To download the free printable for this science experiment, click here .

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Practical Biology

A collection of experiments that demonstrate biological concepts and processes.

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Practical Work for Learning

Published experiments

Identifying the conditions needed for photosynthesis, class practical.

This protocol isolates the contributions of three of the four requirements for photosynthesis in leaves: it shows that chlorophyll, light and carbon dioxide are all necessary for starch to form in leaves.

Lesson organisation

Practise the technique of testing leaves for starch before setting up this practical. If you can set it up at the end of one session, you will be able to test the leaves the following day.

If you have enough plants of each type and enough time, each pair of student could test leaves that have been exposed to all four treatments. Keeping track of four leaves with different treatments for starch testing can be a challenge! If not, each pair could test leaves for one condition being investigated and results could be pooled for the class.

Apparatus and Chemicals

Details of the apparatus and chemicals needed to test the leaves for starch are in Testing leaves for starch: the technique

Additional apparatus only is listed here.

For each group of students:

Black paper or aluminium foil, in strips 2 – 3 cm wide and long enough to wrap around both sides of a leaf

Paperclips, 2

Marker pen to label tubes if electric hot water bath is used

For the class – set up by technician/ teacher:

Plants, variegated and fully green, de-starched by keeping in the dark for 48 hours ( Note 1 )

Plants for investigation 3

Bell jar, covering a de-starched plant, and a beaker of soda lime ( Note 2 ), secured to a glass plate or plastic tray with Vaseline or silicone grease

Bell jar, covering a de-starched plant, and a beaker containing hydrochloric acid and marble chips ( Note 3 ), secured to a glass plate or plastic tray with vaseline or silicone grease

Health & Safety and Technical notes

See also Health and safety guidelines in Testing leaves for starch: the technique .

Read our standard health & safety guidance

1 You can de-starch a plant by placing it in a dark cupboard, or placing it under a bell jar and draping black paper or cloth over the bell jar. It takes about 48 hours for a pelargonium (pot geranium) to use up the starch stored in its leaves.

2 Soda lime absorbs carbon dioxide from the air. Refer to CLEAPSS Hazcard 91 for more details. It is corrosive. Check the first aid procedure if anyone should get soda lime in their eye. 1 cm depth of granular soda lime in a 100 cm 3 beaker, or in a Petri dish (which has a larger surface area if there is room) under the bell jar will absorb the carbon dioxide from the atmosphere. Carbosorb ® is a self-indicating carbon dioxide absorber which is more efficient than soda lime, but more expensive.

3 Marble chips (10 – 20 chips) will produce carbon dioxide if you add some hydrochloric acid. Add about 50 cm 3 of 0.1 M acid to a 250 cm 3 beaker containing marble chips. The chips will effervesce for a while as the carbon dioxide is released. Refer to Hazcard 47A: hydrochloric acid is an irritant at concentrations about 2.0 M but is low hazard at this concentration.

Ethical issues

There are no ethical issues associated with this procedure.

SAFETY: Only the teacher/ technician should handle the soda lime.

Preparation

a Keep enough plants for the investigation in a dark place for 48 hours so that they use up their stored starch.

b Test a few leaves from the de-starched plants to show that they contain no starch before the different treatments.

Investigation 1

c Place a de-starched variegated plant on a sunny windowsill for 24 hours. In the winter you may need additional illumination from an artificial source such as a halogen lamp.

d Remove a variegated leaf. Trace its outline on a piece of paper and draw the pattern of white/green patches.

e Test the leaf for starch using the procedure practised before.

f Draw the pattern of starch-containing cells that show with iodine solution. Compare this pattern with the original pattern of white/green patches.

Investigation 2

g Several groups of students can use the same plant for this procedure, by covering parts of different leaves.

h Take a strip of black paper or aluminium foil and fold it in half. Mark the paper or foil with your initials, or, if there is time, cut a shape out of the paper or foil.

i Place the paper or foil over the leaf so that it covers part of the leaf on both sides. Use two paperclips to secure it gently in place, so that it is in close contact with the leaf surface. If the paper or foil does not actually touch the leaf, light can get in around the edges and make the result less clear.

j Put the plant on a sunny windowsill for 24 hours.

k Remove the covered leaves. Remove the paper or foil and test the leaves for starch using the procedure practised before.

l Draw the pattern of starch-containing cells that show with iodine solution. Compare this pattern with the position of the paper or foil.

Investigation 3

Set up by teacher/ technician 

j Think about the differences between the two bell jars set up by the teacher/ technician. One contains carbon dioxide in the air and the other doesn’t. Place both is a sunny position for 24 hours.

k Test a leaf from each plant and note which contains starch.

Teaching notes

Expected results

Investigation 1 – the pattern of starch-containing cells should follow the pattern of chlorophyll containing cells – starch will only be made where the leaf contains chlorophyll and can photosynthesise.

Investigation 2 – the pattern of starch-containing cells should follow the pattern of the paper or foil used to cover the leaf. Areas left uncovered should contain starch, and areas that were covered should not. Starch will only be made where the leaf has received light and has photosynthesised.

Investigation 3 – the plant kept in an atmosphere of reduced carbon dioxide will not have been able to produce starch by photosynthesis but the plant in the enriched atmosphere will be able to produce starch.

Health & Safety checked, December 2008

Related experiments and Standard procedures

Testing leaves for starch: the technique Practise the techniques for testing leaves for starch in a teaching session before running the practical that identifies the conditions needed for photosynthesis.

Investigating factors affecting the rate of photosynthesis This procedure allows you to quantify the effect of some of the factors that affect the rate of photosynthesis by following the changing rate of photosynthesis in pond weed as conditions such as temperature, carbon dioxide concentration and light intensity change.

Investigating photosynthesis using immobilised algae This procedure uses a more sophisticated method to follow the process of photosynthesis by directly measuring the changes in carbon dioxide levels caused by photosynthetic activity.

• Biology Article
• Experimentally Show That Carbon Dioxide Is Given Out During Respiration

Experiment To Prove That Carbon Dioxide Is Given Out During Respiration

One of the basic and fundamental life processes that are carried out by living entities is respiration. It is a catabolic process wherein complex organic molecules are broken down into simpler molecules. The process releases energy either in the absence or presence of oxygen, and hence respiration can be of two kinds:

• Aerobic respiration – This kind of respiration takes place in the presence of oxygen, hence it results in the complete glucose oxidation with the release of energy. It includes three stages – namely, Krebs cycle, ETS and Glycolysis. All events relating to ETS take place inside mitochondria while stages connected with glycolysis take place in the cytoplasm.
• Anaerobic respiration – In this type of respiration, oxidation of food takes place in an environment lacking oxygen supply. Less energy is released as a result of incomplete oxidation of glucose.

See Also: Differences Between Catabolism and Anabolism

To experimentally demonstrate that carbon dioxide is released during the process of respiration.

Principle/Theory

The process of respiration is biochemically carried out wherein food, glucose to be precise, is oxidized and energy is released. In this experiment, gram seeds (moistened) are used. The purpose of using these seeds is that they release carbon dioxide and are respiring actively. The released carbon dioxide is consumed by the solution of KOH.

Material Required

• Soaked gram seeds
• U-shaped delivery tube
• Conical flask
• Blotting paper (moist) /cotton wool
• Rubber cork with a single hole
• Freshly prepared KOH solution (20%)
• Germinate close to 25 seeds. This can be done by wrapping them in moist blotting paper or cotton wool for around 3 to 4 days.
• Set up the germinated or sprouted seeds in the conical flask. Spray some water into the flask to dampen the seeds.
• With the help of a thread, suspend the conical flask containing the test tube having a freshly prepared 20% KOH solution.
• Use the rubber cork to seal the opening of the conical flask.
• One edge of the U-shaped glass delivery tube present in the conical flask should be inserted through the hole in the rubber cork. The other edge should be placed into a beaker that is saturated with water.
• All attachments of the set-up should be sealed. This can be done using vaseline to create an air-tight environment.
• The initial water level present in the U-shaped delivery tube needs to be marked.
• Leave the experimental set-up uninterrupted for 1 to 2 hours. Observe the fluctuations in the water level in the tube.

Observation

Careful observation after a certain period of time reveals that the water level in the U-shaped delivery tube has risen in the beaker.

Conclusions

The rise in level water indicates that carbon dioxide is released as a result of germinating gram seeds during the process of respiration in the conical flask. The carbon dioxide that is released in the process is absorbed or consumed by the KOH solution that is suspended in the test tube in the conical flask, creating a vacuum or a void in the flask resulting in the upward water movement in the tube. Hence, the water level in the tube changes.

Precautions

• The seeds that are to be germinated need to be moistened
• Air-tight environment for all the connections in the experimental set-up
• The KOH solution that is used needs to be freshly prepared
• Care needs to be taken to ensure that one end of the delivery tube is placed in the conical flask. The other edge is submerged in the water of the beaker
• The tube that contains the KOH solution needs to be suspended carefully

Viva Questions

Q.1. Why is the energy output of the anaerobic respiration lesser than aerobic respiration?

A.1. The process of anaerobic respiration produces 2 ATP. Aerobic respiration, on the other hand, produces 38 ATP involving complete oxidation of glucose. In anaerobic respiration, glucose is partially broken down.

Q.2. List the levels of aerobic respiration.

A.2. The following are the levels in aerobic respiration:

• Krebs cycle
• Oxidative phosphorylation and ETS

Q.3. The cells’ energy currency is _________

A.3 Adenosine triphosphate (ATP)

Q.4. What happens when the photosynthesis rate is equal to the respiration rate?

A.4. When both are equal, it enters into a compensation point where there is no gross gas exchange taking place.

Q.5. Can plants respire and take part in photosynthesis?

A.5 Yes, plants can respire in addition to taking part in photosynthesis during the day time.

Q.6. What is the purpose of keeping the seeds moistened in the experiment?

A.6. Seeds are required to be moist as water is required for growth to germinate. If they are not moist enough, they may dry up resulting in a dip in the respiration rate.

Q.7. Can boiled seeds be used in place of moistened germinating seeds?

A.7. No, they cannot be used as boiled seeds cannot undergo respiration. The experiment will show no result.

Q.8. State the significance of using KOH solution in the experiment.

A.8. The solution is known to absorb carbon dioxide that is released during the process of respiration of germinating seeds, thereby creating a slight vacuum in the flask hence increase in the water level. The rise in water level indicates the occurrence of the process of respiration.

Q.9. List one circumstance under which there would be no rise in the water level in the apparatus.

A.9. If the test tube holding the KOH solution is discarded from the experimental setup, the carbon dioxide produced during the respiration process shall not be consumed hence there would be no inflation in the water level.

Q.10. In the experiment, what is the purpose of using Vaseline?

A.10. It is used because it is used to seal all the apparatus, hence securing the set-up air-tight.

Q.11. Can you think of an alternate method to depict the release of carbon dioxide during the respiration process?

A.11. In the same apparatus, water could be replaced by lime water as lime water tends to turn milky in the presence of carbon dioxide.

Q.12. What are respiratory gases?

A.12. Carbon dioxide and oxygen are involved in the process of respiration, and hence are known as respiratory gases.

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provide diagram and video too

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